Saw tooth voltage generator



Dec. 8, 1953 3, LE co 2,662,197

SAW TOOTH VOLTAGE GENERATOR Filed Feb. 15, 1949 I l J-azmaz 401711109) 907%; #70071! MRI/ll 12465 IN V EN TOR. doaszumlz''om AGENZ'.

RBI SYSZZ'M Patented cc. 8, i953 SAW TOOTH VOLTAGE GENERATOR Corstiaan Le Comte, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust. Company, Hartford, Conn, as trustee Application February 15, 1949, Serial No. 76,464

Claims priority, application Netherlands April 6, 1948 8 Claims.

nected to it the series combination of an anode resistance of the tube, a condenser and a sec.- ond resistance, the control-grid of the tube being connected via the second resistance and an auxiliary voltage source to the cathode of the tube, the said condenser being connected as a negative feedback condenser between the anode and the. control-grid of the tube and the pulse-shaped voltage to be integrated being supplied by the auxiliary voltage source which is caused to operate in the rhythm of the sawtooth oscillation. to be produced.

According to the invention, the practical ranges of possible employment of theabove described devices are materially extended by choosing the supply voltages of the tube to be. such that when the auxiliary voltage source isinoperative, an appreciable anode rest current occurs, so that when a constant auxiliary voltage of negative polarity becomes effective the anode potential increases substantially linearly with time.

In the devices assumed in the foregoing asbeing known, the anode rest current of the. electron tube, which as a rule, operates as a switch, is zero or very low, and it can only be ensured that the anode potential decreases linearly withtime.

By adjusting the tube, in accordance with a.

further feature of the invention, as a class-A amplifier it is ensured that, when a constant auxiliary voltage becomes effective the anode potential varies substantially linearly with time in a sense varying with the polarity of the auxiliary voltage. By a class A amplifier ismeant one in which the grid bias voltage permits a steady anode current flow of such value thatthe anode current varies directly as the grid voltage for the complete cycle of 360 degrees. The resulting output voltage for an ideal class A amplifier is an exact reproduction of the grid voltage.

The latter adjustment, the class-A amplifier adjustment, is particularly suitable for use in 2 radar apparatus in which, for scanning the image screen of the polar position indicator in the direction of. a rotating radius vector use is made of sawtooth deflection voltages which are modulated by quadrature sinusoidal alternating voltages. The defiection voltages required for this purpose are produced with the use of two devices according to the invention by employing therein, two quadrature sinusoidal alternating voltages as auxiliary voltages.

In order that the invention may be. more clear- 1y understood, and readily carried into eiiect, it

will now be described more fully with reference a to the accompanying drawing.

F g. 1 shows one embodiment of the device ac cording to theinvention in itssimplestiorm and Figs. 2, 3 and 4 show associated diagrams i1- lustrating the. adjustment and the. operation.

Fig-5 showsa device according to the invention whciichv has been found to be useful in practice an Figs. 6 and '7 show diagrams illustrating Fig. 5.

Fig. 8 is a block diagram of a polar position indicatorxfor a radar system.

In the device shown in. Fig- 1 a pentode electron tube, i is connected to an anode voltage source 2. The anode lead. of the. tube comprises an anode resistance 3, which is connected in series witha negative feedback condenser ii con nected. between anode and control-grid of the tube, a. grid. resistance 5. and. an auxiliary voltage source 6'. The. series combination of the grid resistance. 5 and. the auxiliary voltage source 6 is shunted bya short-circuiting switch '11 which is closed in. rest. position of the device. The con-- trol-grid circuit of the electron tube comprises in addition a. grid bias voltage source 8 which serves to. adjust. the. working point of the tube l in rest position.

Fig. 2 shows. the. variation of the anode current; (In). of. the tubewith the control-grid voltage (Vg) According to the invention, the value of the control-grid bias voltage supplied by battery 8. is chosen to be such that with the shortcircuiting switch 7- closed in rest position an appreciable anode rest current occurs in the tube I; for example the anode rest current may correspond to the working point designated ii in Fig. 2, if only sawtooth voltages varying in a positive sense are required to be produced, or else the working point may correspond to point it of Fig. 2 so long as the polarity of the sawtooth voltage to be produced alternates.

Starting with the rest position and the associ'ated adjusted working point it, the operation of the circuit shown in Fig. 1 may be described as follows. If the auxiliary voltage is negativegoing and is independent of time, the potential of the control-grid, on the short-circuiting switch l being opened, will be decreased owing to the auxiliary voltage source becoming operative. This decrease in control-grid potential entails a decrease in anode current of the tube l and h nce an increase in anode potential. This increase in anode potential is transmitted by the negative feedback condenser s to the control-grid of the tube i and counteracts the initial variation of the control-grid potential in such manner that the latter varies to a very small extent and the anode potential varies directly as time. The rate of variation of the anodeand controlgrid potential is determined by the time constant of the circuit of the condenser t, which is chiefly determined by the value of the condenser d and that of the resistance 5 so long as the amplification factor of tube I is sufficiently high. Particularly if the auxiliary voltage considerably exceeds the variation of the grid potential, the following relation obtains for the variation of the anode potential:

dz "R in which Va designates the potential difference between anode and cathode of the tube 3, V1

the value of the auxiliary voltage and R and C the values of resistance and condenser d re spectively.

As may be seen from the above relation, the variation of the anode potential is directly proportional to the value of the auxiliary voltage, and is of opposite polarity. The latter fact is made use of, in accordance with the invention, to produce a sawtooth voltage varying in a positive or a negative sense by choice of the polarity of the auxiliary voltage which is periodically caused to be effective.

Referring to Fig. 1, the sawtooth voltage occurs across output terminals it, which are connected to an output resistance ii and of which one is earthed, the other being connected to the anode of tube I by way of a coupling condenser I3.

If, as is shown in the time diagram of Fig. 3a, the short-circuiting switch a is opened for a period t1-t2 the anode potential Va varies, according to the time diagram of Fig. 3b, linearly with time during the said period, the anode potential being increased if the auxiliary voltage is negative. On the switch i being closed at the instant t2. the anode potential is rapidly decreased to the initial value. The maximum amplitude of the sawtooth voltage occurring is proportional to the value of the auxiliary voltage applied. Referring to Fig. 3b, a full line a denotes the variation of the sawtooth voltage with approximately maximum permissible amplitude, which is reached, for example, when the auxiliary voltage is -200 volts, whereas a dotted line b shows the sawtooth voltage when use is made of an auxiliary voltage of 80 volts. In both cases the anode voltage source may supply a voltage of, say, 250 volts. In rest position the working point corresponds to point 9 of Fig. 2.

Fig. 4 shows time diagrams in which in rest position the working point of tube i corresponds to point so of Fig. 2. If, as shown in Fig. 4a, the short-circuiting switch 7 is opened for a period t1t2, the anode potential of the tube varies in accordance with the full line 0 ofthe 4 diagram :32) if use is made of an auxiliary voltage of, for example, 1G0 volts, and in accordance with dotted line d if use is made of an auxiliary voltage volts.

Fig. 5 shows a circuit-arrangement of a device according to the invention for producing alternating sawtooth voltages modulated by a sinusoidal alternating voltage, said arrangement having been found to be preferred in practice. The anode voltage source 2 has again connected to it the series combination of an anode resistance 3, a negative feedback condenser i, a grid resistance ii and an auxiliary voltage source, the latter supplying an alternating sinusoidal voltage and being designated 6. The grid bias battery 8 of Fig. l is replaced by a cathode resistance 8' included in the cathode lead of tube l and shunted by a smoothing condenser 8". The output voltage is taken from the anode of tube i through a coupling condenser 13 and fed to an output resistance ii having output terminals E2.

The grid resistance 5 and the auxiliary voltage source ii are connected in parallel with two diodes id, to having series resistances l5, ii and acting as the short-circuiting switch 7 of Fig. 1. The diodes hi, it are connected in parallel and in opposite senses and, in rest position of the device, stabilise the working point of the tube in accordance with the grid bias supplied by the cathode resistance 8', in such manner that tube 5 is adjusted as a class-A amplifier. The two diodes id, id are periodically out off simultaneously by pulse-shaped voltages of opposite polarity fed to them across connecting terminals i3, it as shown in the figure. The anode potential of the tube l thus varies periodically in sawtooth form in a manner similar to that explained with reference to the preceding figures, the maximum amplitude of the sawtooth oscillations produced varying, however, since the auxiliary voltage varies sinusoidally with time, in accordance with the variation of the auxiliary sine voltage in the manner shown in Fig. 6. As may be seen therefrom and will be obvious from comparison with Fig. 4, the sawtooth voltage is invariably increased linearly with time during one half wave of the auxiliary sine voltage and is invariably decreased linearly with time during the next following half wave of the auxiliary sine voltage.

By using two devices as shown in Fig. 5 with the use of quadrature sine voltages as auxiliary voltages for the two devices, sawtooth voltages are produced which are modulated by the said auxiliary voltages and which are consequently particularly suitable for use as deflection voltages for scanning the image screen of a polar position indicator in a radar apparatus in the direction of a rotating radius vector. Such an arrangement is illustrated in Fig. 8.

If the output sawtooth voltage is taken from the anode of tube 5 through a coupling condenser, the position of the Zero axis of the alternating output voltage relatively to the starting points of the linearly varying flanks of the sawtooth voltage must, however, be allowed for. For use in radar apparatus it is frequently desirable for the said starting points to be located on the said zero axis. The di ect current component which with a view to obtaining the object is to be added to the output voltage and which varies with the value of the auxiliary voltage can be produced, in the device according to the invention, in a particularly simple manner by con-.;-.

nesting, in series with the negative feedback condenser, between the anode and the control-grid of tube an auxiliary resistance 2.0, the value of which is suitably chosen relatively to the grid resistance 5. This resistance has the effect that during the flanks of the generated sawtooth voltage varying linearly with time the output voltage has to it a supplementary voltage of constant value, which constitutes such a fraction or" the auxiliary voltage 6 as is determined by the ratio between resistance 2c and the grid resistance 5. By adjusting the value of the resistance 2d at any constant value of the auxiliary voltage 6' in such manner that the desired position of the zero axis of the output voltage is obtained, this favourable position of the zero axis of the output voltage will also occur automatically at other values of the auxiliary voltage, as is shown in Fig. 7 by a full line and a dotted line (e and I respectively) for output voltages of widely different values at a constant value of the resistance 28.

What I claim is:

1. Apparatus for generating a sawtooth voltage having a predetermined frequency comprising an electron discharge tube having a cathode, a control grid and an anode, an anode resistance, a grid resistance, means to apply a constant positive voltage relative to said cathode to said anode through said anode resistance, means to apply a constant negative voltage relative to said cathode to said grid through said grid resistance, a negative feedback capacitance connected between said anode and said grid, a source of auxiliary voltage interposed between said grid resistance and said cathode, and means periodically to render said auxiliary source alternately operative and inoperative with respect to said grid at a rate corrmponding to said predetermined frequency, said constant positive and negative voltages having respective magnitudes at which an appreciable anode current flows through said tube in the intervals in which said source is inoperative whereby an anode current varying linearly with time is produced in the intervals in which the source is operative.

2. Apparatus for generating a sawtooth voltage having a predetermined frequency comprising an electron discharge tube having a cathode, a control grid and an anode, an anode resistance, a grid resistance, means to apply a constant positive voltage relative to said cathode to said anode through said anode resistance, means to apply a constant negative voltage relative to said cathode to said grid through said grid resistance, a negative feedback capacitance connected between said anode and said grid, a source of auxiliary voltage interposed serially between said grid resistance and said cathode, and switching means bridging said serially connected source and grid resistance periodically to render said auxiliary source alternately operative and inoperative with respect to said grid at a rate corresponding to said predetermined frequency, said constant positive and negative voltages having respective magnitudes at which an appreciable anode current flows through said tube in the intervals in which said source is inoperative whereby an anode current Varying linearly with time is produced in the intervals in which the source is operative, said auxiliary voltage being constituted by an alternating potential whose frequency is small with respect to said predetermined frequency.

3. Apparatus for generating a sawtooth volt? age having a predetermined frequency comprising an electron discharge tube having a cathode, a control grid and an anode, an anode resistance, a grid resistance, means to apply a constant positive voltage relative to said cathode to said anode through said anode resistance, means to apply a constant negative voltage relative to said cathode to said grid through said grid resistance, a negative feedback capacitance connected between said anode and said grid, a source of auxiliary voltage interposed between said grid re.- sistance and said cathode, means periodically to render said auxiliary source alternately operative and inoperative with respect to said grid at a rate corresponding to said predetermined frequency, said constant positive and negative voltages having respective magnitudes at which said tube acts as a class A amplifier, whereby an anode current varying linearly with time is pro? duced in the intervals in which the source is operative, and an output circuit coupled to said anode to derive the sawtooth voltage therefrom.

l. Apparatus for generating a sawtooth voltage having a predetermined frequency comprise ing an electron discharge tube having a oaths ode, a control grid and an anode, an anode resistance, a grid resistance, a. constant voltage supply having a positive terminal connected through said anode resistance to said anode and a negative terminal connected to said cathode, a resistor-condenser parallel network connected at one end to said cathode and at the other end through said grid resistance to said grid to provide a bias voltage therefor, said constant voltage and said bias voltage having re.- spective magnitudes at which said tube operates as a class A amplifier, a negative feedback capacitance connected between said anode and said grid, an auxiliary voltage source interposed between said grid resistance and said network, and means periodically to render said auxiliary source alternately operative and inoperative with respect to said grid at a rate corresponding to said predetermined frequency.

5. Apparatus for generating a sawtooth voltage having a predetermined frequency con1prising an electron discharge tube having a cathode, a control grid and an anode, an anode resistance, a grid resistance, a constant voltage supply having a positive terminal connected through said anode resistance to said anode and a negative terminal connected to said cathode, a resistor-condenser parallel network connected at one end to said cathode and at the other end through said grid resistance to said grid to provide a bias voltage therefor, said constant anode voltage and said bias voltage having respective magnitudes at which said tube operates as a class A amplifier, a negative feedback capacitance connected between said anode and said grid, an auxiliary voltage source interposed between said grid resistance and said network, and means periodically to render said auxiliary source alternately operative and inoperative with respect to said grid at a rate corresponding to said predetermined frequency, said last named means including a, diode connected across the series circuit formed by said auxiliary source and said grid resistance, and means to apply rectangular pulses to said diode to render it periodically conductive.

6. Apparatus for generating a sawtooth voltage having a predetermined frequency comprising an electron discharge tube having a cathode, a control grid and an anode, an anode resistance, a grid resistance, a constant voltage supply having a positive terminal connected through said anode resistance to said anode and a negative terminal connected to said cathode, a resistor-condenser parallel network connected at one end to said cathode and at the other end through said grid resistance to said grid to provide a bias voltage, said. constant voltage and said bias voltage having respective magnitudes at which said tube operates as a class A amplifier, a negative feedback capacitance connected between said anode and said grid, an auxiliary alternating voltage source interposed between said grid resistance and said network and having a frequency which is small with respect to said predetermined frequency, and means periodically to render said auxiliary source alternately operative and inoperative with respect to said grid at a rate corresponding to said predetermined frequency and including a pair of diodes connectec in parallel opposition across the series circuit formed by the series connected grid resistance and auxiliary source and means to apply periodic rectangular pulses in phase opposition to said diodes to render said diodes simultaneously conductive periodically at a rate cor responding to said predetermined frequency.

'7. Apparatus for generating a sawtooth voltage having a predetermined frequency comprising an electron discharge tube having a cathode, a control grid and an anode, an anode resistance, a grid resistance, a constant voltage supply having a negative terminal connected to said cathode and a positive terminal connected through said anode resistance to said anode, means to apply a constant negative voltage relative to said cathode to said grid through said grid resistance, said constant voltages having respective magnitudes at which said tube operates as a class A amplifier, a negative feedback capacitance connected between said anode and said grid, an auxiliary voltage source interposed between said grid resistance and said cathode, means periodically to render said source alternately operative and inoperative with respect to said grid at a rate corresponding to said predetermined frequency, an output circuit for deriving the sawtooth voltage from said anode and including a coupling capacitor connected to said anode, and means for varying the direct-current component of the sawtooth voltage including a variable resistance interposed between said grid and said negative feedback capacitance.

8. In a plan position indicating radar system provided with a cathode-ray tube having first and second deflection means, apparatus for gencrating first and second deflection voltages to be applied to said deflection means, said apparatus being constituted by two sawtooth generators operating at a predetermined frequency each having an electron discharge tube including a cathode, a control grid an an anode, an an anode resistance, a grid resistanc. a 6011 stant voltage supply having a positive terminal connected through said anode resistance to said anode and a negative terminal connected to said cathode, a resistor-condenser p rallel network connected at one end to said cathode and at the other end through said grid resist 166 to said grid to provide a bias voltage thereior, constant voltageand said bias voltage having spective magnitudes at when said tube 0; rates as a class A amplifier, ne ive feedback capacitance connected between said grid, an auxiliary voltage source interposed between said grid resistance and said network and means periodically to render "l auxiliary source alternately operative and inoper ative respect to said at a rate corresponding to said predetermined frequency, the auxiliary voltages of the two generators being constituted by two alternating sine voltages in phase quadrature whose frequency corresponds to the scanning rate of the plan position indicating systez' COPSTIAAE? Gill /FIE.

iteferences Gited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Wireless World, June 1946, pages rid-1T6. 

